The field of this invention is removal of solid particulate matter from hot gas, such as is formed during coal gasification.
Gases containing molten ash or slag droplets often present difficulties in processing, because deposits tended to build up on walls, valves and outlets of the processing equipment and interfered with good operation, even leading to complete blocking of the equipment. Although sometimes molten contaminants in a gas were so thinly liquid, i.e., non-viscous, that removal of the greater part thereof did not cause problems, as a rule a mist of molten particles remained behind in the gas, which, upon cooling, became sticky and then tended to cause the processing difficulties mentioned.
These sticky particles could be completely or partly in the molten state and they could comprise metals and salts. When cooled down to a sufficiently low temperature these particles would completely solidify or at least become so solidified of stiff that their stickiness disappeared. Once the particles could be lowered in temperature to a level where they were no longer sticky, they could be removed by known mechanical techniques such as cyclones, bend separators, filters and similar devices. However, a wide melting range over which the particles were sticky rather than one melting point was often involved, so such a melting range could in some instances even cover hundreds of degrees centigrade.
An important process in which such sticky particles are formed is the manufacture of gases containing carbon monoxide by incomplete combustion of ash-containing coal. Upon combustion of coal in a reactor, the ash in the coal produced slag. On leaving the reactor, the gas produced by combustion usually had a temperature at which the ash had a high fluidity, e.g. a temperature higher than 1300.degree. C., and the emerging gas thus contained a mist of molten slag particles. For further processing the crude product gas had to be cooled down to a lower temperature, e.g. 100.degree. C. The molten particles from coal usually became sticky in the temperature range from 900.degree.-1500.degree. C., so that the difficulties with deposits building up in processing equipment tended to arise as the product gas was cooled for further processing.